A CO2 two-phase thermosyphon loop (TPTL) system in data centers were investigated in this study. The maximum heat transfer capacity

total thermal resistance

and driving temperature difference were compared between CO2 and R22 TPTLs experimentally. The results indicate that under the same filling ratio

the maximum heat transfer capacity of CO2 TPTL was significantly greater than that of R22 TPTL. When the diameters of the riser and downcomer were 9 mm

the maximum heat transfer capacities of the CO2 and R22 TPTLs were 3 300 W and 1 500 W

respectively. When the diameter was 12 mm

the maximum heat transfer capacity of the CO2 and R22 TPTLs were 5 400 W and 2 200 W

respectively. The study also found that the normal working load range of CO2 TPTL was larger than that of R22 TPTL

but the total thermal resistance of CO2 TPTL was lower than that of R22 TPTL. Under different heat transfer capabilities

the driving temperature difference required for CO2 TPTL was 4 °C lower than that of R22 TPTL on average; that is

the cooling source temperature required by CO2 TPTL can be increased by 4 °C under the same conditions. Taking a small data center as an example

it was calculated that the annual energy consumption of the CO2 TPTL system is 7.425 × 105 kW?h lower than that of the R22 TPTL system and 3.182 × 106 kW?h lower than the central air-conditioning system under the climate conditions in Shanghai. Keywords two-phase thermosyphon loop; CO2; data center; filling ratio